Conventionally, a membrane separation active sludge treating method has been known as a method of treating wastewater (water to be treated) such as sewage, industrial wastewater, household wastewater and others.
In this membrane separation active sludge treating method, an immersion type membrane separation apparatus is immersed and installed in a reaction tank for treating wastewater by active sludge treatment. This immersion type membrane separation apparatus is composed by disposing a plurality of membrane elements A′ of organic flat membrane type in parallel at specified intervals in a main body casing as shown in FIG. 7, and by disposing the surfaces of filtration membranes F along the vertical direction to fill. The wastewater is sucked and filtered by making use of a negative pressure (inter-membrane differential pressure) generated in the membrane elements A′ from the surfaces of filtration membranes F between membrane elements A′, and the filtered water is taken out as a treated water.
Moreover, an aeration device is disposed in the bottom of the reaction tank at a lower position from the immersion type membrane separation apparatus immersed in the reaction tank, and the membrane elements disposed hi parallel are agitated within the tank by generating an ascending stream in the wastewater by elevating a membrane cleaning gas (generally, air), so that the surface of the membrane elements may be cleaned.
However, the conventional membrane elements A′ are long and rectangular in shape, and are composed by merely bonding the peripheral edges of the filtration membranes F to the surface of a membrane element main body part 1′, and when a suction pressure or feeding pressure is applied to the filtration membranes F at the time of filtering or chemical cleaning, the filtration membranes F may be loosened or deviated, and the adjacent filtration membranes F may contact with each other when the filtration membranes F are disposed oppositely, and filtering or chemical cleaning may not be carried out uniformly along the entire surface of the filtration membranes F, and the efficiency of filtering or chemical cleaning may be lowered.
Moreover, the bonding force of the filtration membranes F to the surface of the membrane element main body part l′ is limited, and it is difficult to raise the flow velocity at the time of filtering or chemical cleaning.
This problem is a bottleneck for increasing the size of (increasing the surface area of) the membrane elements A′.
Moreover, the conventional membrane elements A′ are generally long and rectangular in shape, and are designed to such the wastewater (water to be treated) in the reaction tank by the entire membrane surface, and therefore, at the time of suction, the suction pressure may be deviated on the entire membrane surface, and the wastewater may not be filtered efficiently.
To solve this problem, a route of filtered water is formed by cutting a recess or a groove in the membrane surface, but since only one discharge port is provided to discharge water, at the time of suction of wastewater, its suction pressure is concentrated around the discharge port, and at the time of sucking and filtering, the suction force is concentrated in a portion closer to the discharge port, and, as a result, uniform filtering on the entire membrane surface is not realized.
In the invention as disclosed in patent document 1, by varying the coefficient of resistance of the liquid collecting portion and the liquid passing route, for example, the coefficient of resistance of the route network in an immediate region contacting with the liquid collecting portion is set smaller than the coefficient of resistance of the route network remoter from the immediate region, or the coefficient of resistance is decreased in the route network closer to the liquid collecting portion, sequentially or at gradual steps or intermittently, so that a uniform filtering may be realized on the entire membrane element surface.
However, in the configuration disclosed in patent document 1, same as in the membrane elements shown in FIG. 7, since the inside of the membrane element is not divided, but is used as one whole membrane surface, if clogging occurs in a part of the membrane surface, the suction amount is changed by this clogging, and the predetermined coefficient of resistance of the entire membrane surface is changed, and uniform filtering cannot be executed as specified.
[Prior Art Literature]
[Patent Document]
Patent document 1: Japanese Patent Application Laid-Open No. 2008-246356